Container linings



g- 1961 P. G. GRANFORS 2,998,374

CONTAINER LININGS Filed Feb. 9, 1959 0 G O O o FIG. 2

l5 /NEOPRENE rPOLYlSOPRENE JNEOPRENE IN V EN TOR.

PAUL s. GRANFORS BY FIG. 3

2,998,374 CONTAINER LININGS Paul G. Granfors, Akron, Ohio, assignor to The Goodyear Tire & Rubber Company, Akron, Ohio, a corporation of Ohio Filed Feb. 9, 1959, Ser. No. 791,967 7 Claims. (Cl. 204250) This invention relates to improved electrolytic cell covers and is particularly concerned with chlorine cell covers comprised of particular elastomeric laminates.

Halogens such as chlorine, fluorine, etc., may be prepared by a continuous electrolytic process wherein an anode, e.g., graphite, and a cathode, e.g., mercury, are suspended in a water solution of the metallic salt of the desired halogen, e.g., NaCl, after which a high electric current, e.g., 25,000 to 30,000 amperes, is passed through the brine. The ionized halogen migrates to the anode where two atoms combine to make a molecule which is discharged from the salt solution and recovered through a vacuum line. The free metal dissolves in the mercury cathode to form an amalgam which floats on the mercury and can therefore be withdrawn from the cell. The electrolytic process is further described in Chemical Engineering Process, vol. 46, No. 9, page 440 et seq., September 1950.

The free halogen will normally contain a quantity of water from the brine which results in the formation of very corrosive compounds, e.g., HOCl. Because very high electrical currents are necessary in the electrolytic process for producing halogens such as chlorine, the atmosphere about the cell contains a high concentration of ozone which is extremely deleterious to most elastomeric compositions. Thus, electrolytic cell covers are subject to attack from both sides.

The customary anodes and cathodes have a life expectancy of about fifteen months. Prior to this invention, the customary cell covers, which have customarily been made from corrosion-resistant metals and rubber-covered metals, have deteriorated rapidly which has necessitated shut-down of the electrolytic cells periodically for replacement of the cell covers with resultant loss of operating efficiency. The practice of the present invention results in a cell cover which will remain operable over longer periods of time which may be extended until the anodes and cathodes must be replaced.

It is a general object of this invention to provide an improved electrolytic cell cover. It is another object of this invention to provide an improved process for preparing electrolytic cell covers. It is a further object of this invention to provide a corrosion-resistant chlorine cell cover comprised of an elastomeric laminate. It is another object of this invention to provide a process for preparing a chlorine cell cover comprised of two outer layers of neoprene and at least one inner layer of polyisoprene.

In the practice of this invention, a corrosion-resistant cover suitable for use in connection with electrolytic cells is comprised of a laminate having two outer plies comprised of a chlorine permeable elastomeric composition and at least one inner ply comprised of a chlorine impermeable elastomeric composition.

The cell cover is preferably comprised of two layers of polychloroprene ranging in thickness from about one thirty-second of an inch to one-half inch with at least Patented Aug. 29, 1961 one inner ply comprised of polyisoprene about one thirtysecond of an inch to one-half inch thick. Preferably the plies will be about one-sixteenth of an inch to one-fourth of an inch thick. The various plies may be of the same thickness or may be varied in thickness and various other layers of elastomerie compositions may be used in the laminates. Also, multiple layers of polychloroprene and polyisoprene may be employed as long as the outer layers are comprised of polychloroprene.

Non-fully equivalent results may be achieved by substituting chlorosulfonated polyethylene for the polychloroprene and butyl rubber comprised of a major proportion of isobutylene and a minor proportion of isoprene for the polyisoprene.

The invention may be described in connection with the description of the drawings wherein FIG. 1 is a schematic cross section of a typical electrolytic chlorine cell; FIG. 2 is a plan view of a chlorine cell cover of this invention; and FIG. 3 is a cross section of a chlorine cell cover taken along the lines 33 of FIG. 2.

In the customary electrolytic chlorine cell, graphite anodes 11 and mercury cathodes 12 are suspended in a brine 13 which is comprised of a water solution of sodium chloride. In order to provide gaseous chlorine, a high electrical current is passed through line 14 into the anodes in order that a current will pass through the brine. The ionized chlorine will migrate to the anodes 11 and pass through the surface of the brine solution as molecular chlorine. The gaseous chlorine, which contains some water vapor, is thereafter purified and collected.

The cell cover 15 is comprised of a laminate having layers 16 and 17 comprised of a polychloroprene and layer 18 comprised of a polyisoprene. After the laminate is prepared by curing under the influence of heat, holes 19 are punched therein in order that the cell cover may be bolted to the top of the unit.

In the practice of this invention any of the well-known heat-curable neoprenes may be used. Neoprene is a rubbery polymer of a 2-chlorobutadiene-1,3, commonly known as polychloroprene; or rubbery polymers of 2,3- dichlorobutadiene-1,3; or rubbery copolymers of a chlorobutadiene-1,3, with monomers copolymerizable therewith, such as isoprene, butadiene-l,3, styrene, acrylonitrile, etc. The typical neoprenes are known to the trade as W," GN, KN, I, GR N, AC, CG, GR M 10,!1 and others. These neoprenes are more fully described in The Neoprenes by Neil L. Catton, by Rubber Chemicals Division, E. I. du Pont de Nemours and Company, 1953.

The polyisoprene inner layer 18 is comprised of natural rubber or the synthetic rubber, cis 1,4-polymers of isoprene, which may contain up to 15% of the trans polymer and which are similar to natural rubber in structure and use.

In preparing the laminate 15, the various plies will customarily be at least one thirty-second of an inch thick and may vary in thickness or may be the same. The maximum thickness is not particularly critical but should be no more than one-half inch. Preferably, the plies will range in thickness from one-sixteenth of an inch to one-fourth of an inch which provides a laminate having sufiicient rigidity and corrosion resistance and Which can be cured under optimum conditions, to Wit, minimum temperature and time.

In fabricating laminate 15, the various plies may be preferably fabricated by calendering one onto the other or may be made separately and laminated together by means of adhesives. Any of the well-known adhesives such as cyclized rubber cements and natural rubber cements may be used for this purpose. These cements are customarily prepared by dissolving the indicated rubbers in suitable solvents such as gasoline, solvent naphtha; aromatic hydrocarbons such as benzene, toluene, or xylene; or chlorinated solvents such as trichloroethylene or carbon tetrachloride to form the cements. When the laminates are prepared by calendering sheets together, the use of an adhesive is customarily unnecessary.

The rubbers of the various plies of the laminates may be compounded in the customary manner with conventional rubber compounding ingredients such as fillers, curing agents, accelerators, retarders, antioxidants and softeners. In order to accelerate the curing, it is preferable to add a conventional curing agent such as sulfur, an organic peroxide, etc., and one of the customary accelerators such as a thiazole, a dithiocarbamate and/or other known accelerators. Curing may be accomplished by any of the customary methods used for curing rubber sheets. For example, the various plies may be cured in a press either as individual plies or as a laminate or preferably a multiplicity of laminates may be cured in a pot heater by means of steam. Optimum efliciency is obtained by preparing a roll of laminate stock, curing the roll in a pot heater and thereafter cutting the cell covers from the roll. Obviously, the final cutting and punching operation may best be accomplished just prior to use of the laminates as cell covers.

Customarily, the vulcanizing temperature will range from about 200 F. to 350 F. and will usually be from 275 F. to 325 F. The cure time may range from minutes to 24 hours or more and will, of course, depend on the type of stocks being cured, the thickness of the plies and the laminates, and the temperatures employed. Obviously, the higher the temperature, the lower the cure time and vice versa.

The invention is further illustrated by means of the following example which is intended to be illustrative and not a limitation of the invention.

A chlorine cell cover thirty-seven feet ten and onefourth inches long by forty-eight and one-eighth inches wide was prepared by calendering a neoprene W stock to a thickness of .065 inch, thereafter calendering a natural rubber stock .065 inch onto the neoprene stock and thereafter calendering another layer of the same neoprene stock .065 inch thick onto the natural rubber stock having the other neoprene stock calendered onto the opposite side. The neoprene stock was comprised of 100 parts by weight of neoprene type W (polychloroprene), 5 parts by weight of zinc oxide, 2.0 parts by weight of magnesium oxide, 30 parts by weight of calcium silicate, 50 parts by weight of calcium carbonate, 1 part by weight of stearic acid, 1 part by weight of a mixture of aryl paraphenylene diamines, 2 parts by weight of diphenyl amine, part by weight of Du Pont accelerator NA-22 (Z-mercapto imidazoline containing ethylene thiourea), and 5 parts by weight of hydrogenated rosin.

The inner ply was comprised of 100 parts by weight of natural rubber, 6 parts by weight of zinc oxide, 50 parts by weight of clay, 28 parts by weight of fine thermal furnace black, 1 part by weight of stearic acid, 1 part by weight of phenyl beta naphthyl amine, 3 parts by weight of trimethyl dihydro quinoline, 4 parts by weight of tetramethyl thiuram disulfide, 2 parts by weight of mercaptobenzothiazole, 2 parts by weight of litharge, 5

partsby weight of pulverized mineral rubber and 1 part by weight of pulverized hard resin.

After the laminate was made by plying together the three plies of elastomeric composition, the laminate was rolled onto a drum and covered with a water-proof wrapping and thereafter cured by means of steam in a pot heater for minutes at 260 F. followed by 40 minutes at 290 F. followed by 15 minutes at 260 F. When separated by means of a cellophane liner although this was not necessary. After the curing was completed, the laminate was removed from the pot heater and allowed to cool after which holes were made in the laminate in order that the same could be inserted over the top of a commercial chlorine electrolytic cell. Periodic inspection of the cell has indicated that the cover has not deteriorated to any appreciable extent and that the same should last at least as long as the anodes and cathodes. Thus, the practice of the invention has materially improved the efficiency of electrolytic chlorine production.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

I claim:

1. In an electrolytic chlorine cell comprising a container suitable for containing a brine solution, anodes and cathodes positioned to contact said brine solution and through which a sufficient electrical potential may be applied to electrolyze the brine solution, the improvement wherein said cell is equipped with a gas-tight cover consisting of an elastomeric laminate having at least one chlorine impermeable inner ply of polyisoprene and at least one outer ply of neoprene on each side of said inner ply, each of the plies of said laminate being at least one thirty-second of an inch in thickness.

2. An electrolytic cell in accordance with claim 1 wherein the outer plies of the elastomeric gas-tight cover are composed of 2chlorobutadiene-l,3.

3. An electrolytic cell in accordance with claim 1 wherein the outer plies of the elastomeric gas-tight cover are composed of 2,3-dichlorobutadiene-l,3.

4. In an electrolytic chlorine cell comprising a container'suitable for containing a brine solution, anodes and cathodes positioned to contact said brine solution and through which a sufficient electrical potential may be applied to electrolyze the brine solution, the improvement wherein said cell is equipped with a gas-tight cover consisting of an elastomeric laminate having at least one chlorine impermeable inner ply of natural rubber and at least one outer ply of neoprene on each side of said inner ply, each of the plies being from one thirty-second of an inch to one-half inch in thickness and tenaciously ad hered to each adjacent ply.

5. In an electrolytic chlorine cell comprising a container suitable for containing a brine solution, anodes and cathodes positioned to contact said brine solution and through which a sufiicient electrical potential may be applied to electrolyze the brine solution, the improvement wherein said cell is equipped with a gas-tight cover consisting of an elastomeric laminate prepared by plying together at least one chlorine-impermeable inner ply of polyisoprene and at least one outer ply of heat curable neoprene on each side of said inner ply and thereafter heating the laminate to cure the elastomeric composition, each ply of said laminate being at least one thirty-second of an inch in thickness.

6. In an electrolytic chlorine cell comprising a container suitable for containing a brine solution, anodes and cathodes positioned to contact said brine solution and through which a suflicient electrical potential may be applied to electrolyze the brine solution, the improvement wherein said cell is equipped with a gas-tight cover consisting of an elastomeric laminate produced by laminating together an inner ply of pre-cured polyisoprene and an outer ply of pre-cured neoprene on each side of said inner ply, each ply of said laminate being at least one thirtysecond of an inch in thickness.

7. In an electrolytic chlorine cell comprising a container suitable for containing a brine solution, anodes and cathodes positioned to contact said brine solution and through which a s-ufiicient electrical potential may be applied to electrolyze the brine solution, the improvement wherein said cell is equipped with a gas-tight cover consisting of an elastomeric laminate prepared by 1) calendering a sheet of vulcanizable neoprene to a thickness of about one thirty-second inch to one-half inch, (2) calendering a layer of vulcaniz-able polyisoprene about one thirty-second inch to one-half inch thick onto the neoprene layer, (3) calendering another layer of vulcanizable neoprene about one-thirty-second inch to one-half inch thick onto the polyisoprene layer, and (4) curing the laminate at a temperature of about 200 F. to 350 F. for a period ranging from 5 minutes to 24 hours.

References Cited in the file of this patent UNITED STATES PATENTS 2,308,724 Stamberger Jan. 19, 1943 2,366,219 Soday Jan. 2, 1945 2,451,911 Braden Oct. 19, 1948 2,649,134 Steinle Aug. 18, 1953 2,844,502 Paxton July 22, 1958 2,866,731 Epp Dec. 30, 1958 OTHER REFERENCES Fluorine Chemistry, reprint from Industrial & Engineering Chemistry, vol. 39, page 238, March 1947. 

1. IN AN ELECTROLYTIC CHLORINE CELL COMPRISING A CONTAINER SUITABLE FOR CONTAINING A BRINE SOLUTION, ANODES AND CATHODES POSITIONED TO CONTACT SAID BRINE SOLUTION AND THROUGH WHICH A SUFFICIENT ELECTRICAL POTENTIAL MAY BE APPLIED TO ELECTROLYZE THE BRINE SOLUTION, THE IMPROVEMENT WHEREIN SAID CELL IS EQUIPPED WITH A GAS-TIGHT COVER CONSISTING OF AN ELASTOMERIC LAMINATE HAVING AT LEAST ONE CHLORINE IMPERMEABLE INNER PLY OF POLYISOPRENE AND AT LEAST ONE OUTER PLY OF NEOPRENE ON EACH SIDE OF SAID INNER PLY, EACH OF THE PLIES OF SAID LAMINATE BEING AT LEAST ONE THIRTY-SECOND OF AN INCH IN THICKNESS. 